Koompassioxylon, Kramer

Gentis, Nicolas, Licht, Alexis, Boura, Anaïs, Aung, Dario De Franceschi Zaw Win Day Wa & Dupont-Nivet, Guillaume, 2022, Fossil wood from the lower Miocene of Myanmar (Natma Formation): palaeoenvironmental and biogeographic implications, Geodiversitas 44 (28), pp. 853-909 : 866-868

cf. Koompassioxylon

( Fig. 7 )

MATERIEL. — MNHN.F.50182 ; field number: NAT17-06. Estimated minimal diameter: 11 cm .

LOCALITY. — Kalewa Township, Sagaing Region, Myanmar.

AGE. — Upper lower to lowermost middle Miocene.

DESCRIPTION

Wood diffuse-porous. Growth rings indistinct, but possible marginal bands. Vessels mostly solitary (80 %) or grouped by 2 or 3 ( Fig. 7A, C ), oval, 4-9 per mm² (average: 7); tangential diameter 140-250 µm (average: 180 µm; mesured on less compressed vessels but still underestimated). The radial diameter (71-350 µm, average: 225 µm) assumes a large tangential diameter.Tylose absent or rarely present ( Fig. 7C ). Vessel elements 220-460 µm long (average: 300 µm). Perforation plates simple. Intervessel pits alternate, bordered, 6-13 µm (average: 10 µm) in diameter, non-vestured ( Fig. 7G ). Vessel-ray pits rather similar in shape and size to intervessel pits ( Fig. 7I ), 4-11 µm in diameter (average: 7.3 µm). Parenchyma widely aliform and mostly confluent laterally or in diagonal, forming anastomosed shapes, no proper tangential bands ( Fig. 7 A-C); also, maybe in marginal or seemingly marginal thin bands merging with the paratracheal parenchyma; parenchyma cells 50-130 µm long (average: 85 µm), 10-30 µm wide (average: 20 µm); 3-8 (or more?) cells per parenchyma strands ( Fig. 7F ); abundant crystals in chambered parenchyma cells ( Fig. 7H, J ), especially in the margin ones. Rays 1- to 3-seriate (mostly 2-seriate, very few uniseriate) ( Fig. 7E, F ), irregularly storied ( Fig. 7D ) resulting in ripple marks visible with the naked eye, 8-16 rays per mm (average: 11), 150-870 µm (average: 400 µm) or 6-27 cells high (average: 16-17 cells), occasional interconnections of rays ( Fig. 7E ) with alternating uniseriate and 2-3-seriate portions probably resulting from end-to-end fusions, thereby some rays are up to 30 cells high, weakly heterocellular to heterocellular to with mostly one to sometimes 2-3 rows of upright or square cells at both ends ( Fig. 7H ) or at least larger procumbent cells, possibly very rarely with 1-2 crystals in marginal cells; a tendency to have biseriate portions as wide as multiseriate ones, but not to be considered as a distinctive feature. Fibres commonly thin-tothick walled (lumina 0.66 times the double wall thickness) to occasionally very thick-walled, non-septate, 12-24 µm (average: 17 µm) wide.

DISCUSSION

This wood is characterized by: 1) diffuse-porous; 2) aliform parenchyma; 3) crystals in parenchyma cells; 3) mostly 2-seriate rays; 4) non-septate fibres; 5) vessel-ray pits similar to intervessel pits; and 6) simple perforation plates; these features are typical of modern Fabaceae ( Metcalfe & Chalk 1950; Baretta-Huipers 1981; InsideWood 2004 -onward). A search on the InsideWood (2004 -onward) database shows affinities with species from the traditional Caesalpinioideae subfamily because of the number of cells per parenchyma strand that goes up to four cells, compared to hardly exceeding two cells for the traditional Papilionoideae subfamily. Concerning the traditional Mimosoideae, most species have homocellular rays, often septate fibres and rarely storied structures. Nonvestured pits are uncommon in Fabaceae and are restricted to three recircumscribed basal subfamilies: Cercidoideae, Duparquetioideae and Dialioideae ( Herendeen 2000; Gasson et al. 2003; LPWG 2017; Zimmerman et al. 2017), all previously in the traditional Caesalpinioideae subfamily. An investigation of wood anatomy of these subfamilies was made with available literature ( Gasson et al. 2003; InsideWood 2004 -onward; Ogata et al. 2008; Pérez-Lara et al. 2019). Duparquetia Baill. , the only genus of Duparquetioideae, is ruled out as it is a vine with no mineral inclusion and very thin-walled fibres. In Cercidoideae, only Bauhinia (which has a wide range of morphology) can be related to this fossil, but it shows more frequent uniseriate rays, sometimes septate fibres, homocellular rays or regular bands of parenchyma. Moreover, the number of cells per parenchyma strand is restricted to 4 in average in Bauhinia (compared to more than 4 in our fossil). Among Dialioideae, only Kalappia Kosterm. , Koompassia and Martiodendron Gleason share features with our fossil: storied or irregularly storied rays, aliform-confluent parenchyma, 1-3 seriate rays, crystals in parenchyma, at least medium size intervessel pits and heterocellular rays. Kalappia and Martiodendron yet differ in having a strongly storied parenchyma, vessel elements and rays, fewer or more wavy confluent parenchyma, as well as smaller rays for Kalappia (up to 350 µm compared to 400 µm in average in our fossil). Koompassia wood is thus closer to our fossil than the other identified modern analogues, but has more frequent crystals in marginal cells; however, no specific NLR really stands out in regards of the state of preservation of the present fossil.

The fossil genus Tzotziloxylon Pérez-Lara & Estrada-Ruiz (Pérez-Lara et al. 2019) covers fossils sharing features of the Cercidoideae/Dialioideae which includes non-vestured intervessel pits, aliform to occasionally confluent parenchyma as well as diffuse and sometimes banded, 1-4-seriate rays, crystalliferous parenchyma and non-storied structure. Our fossil is thus incompatible with this genus. Among Cercidoideae, woods resembling Bauhinia are described under the name Bauhinia and Bauhinium Trivedi & Panjwani with regularly storied and mostly uniseriate rays as well as regular parenchyma bands

( Ramanujam & Rao 1966; Prakash & Prasad 1984; Trivedi & Panjwani 1986; Awasthi & Prakash 1987; Awasthi & Mehrotra 1990). The diagnosis of these genera is yet incompatible with our specimen. Among Dialioideae, woods resembling Koompassia are described under the name Koompassioxylon ( Kramer 1974; Srivastava & Awasthi 1996). Although most of the features of the genus diagnosis are compatible with our fossil, some differences have to be pointed out: the aliform to confluent parenchyma with only a few vessels, marginal ray cells can be subdivided and contain crystals (presence of which is ambiguous in the present fossil as it is hard to determine if crystals belong to ray cells or the underneath axial parenchyma cells). Moreover, intervessel pits are vestured in previously described specimens of Koompassioxylon . This specimen is different from the K. elegans described above (p. 864) because of the absence of numerous crystals in marginal ray cells, mainly confluent parenchyma and mainly 2-seriate rays. Pending more comprehensive studies about fossil Cercidoideae/Dialioideae and other related Fabaceae , we name it cf. Koompassioxylon to emphasize its close affinity to this genus.

Koompassia ecology has been previously described (p. 864). Kalappia trees reach up to 40 m tall, 90 cm in diameter, and are restricted to wet lowland forests of Sulawesi, up to 300 m (rarely 500 m) altitude ( Hou et al. 1996; Sosef et al. 1998). Martiodendron are South American canopy trees, often riparian, growing in rainforests, periodically inundated forests, but also in tropical savanna woodlands, deciduous or seasonally dry forests, below 600 m altitude ( Koeppen & Iltis 1962; Lewis et al. 2005). These genera have relatively hard and durable wood ( Scheffer & Morrell 1998).

Figures

FIG. 7. — cf. Koompassioxylon, MNHN.F.50182: A, Ts, mostly solitary vessels with aliform and aliform-confluent parenchyma, sometimes forming anastomosed shapes; B, Ts, interpretation of (A) of the parenchyma pattern (dotted) showing mostly confluent parenchyma, aliform parenchyma, but no regular bands; C, Ts, detail of aliform parenchyma and one vessel with tyloses (although rare, arrow); D, Tls, storied tendency of rays (arrows); E, Tls, 1-3 seriate heterocellular rays, sometimes with some rays with alternating uniseriate and mutliseriate portions (arrows); F, Tls, detail of a 2-seriate ray bordered by a strand of parenchyma made of at least eight cells (each marked by arrow); G, Rls, non-vestured (arrows), alternate, polygonal intervessel pits; H, Rls, heterocellular rays, sometimes with upright marginal cells (black arrow) and crystalliferous parenchyma, with more than 11 crystals per strand (white arrow); I, Rls, vessel-ray pits with distinct border (arrows) of the same size and shape as intervessel-pits; J, Tls, detail of crystals in chambered (arrows) parenchyma cells. Scale bars: A, B, 1 mm; D, 500 µm; C, E, F, H, 200 µm; G, I, J, 20 µm. Abbreviations: see Fig. 2.

FIG. 2. — Cupressinoxylon sp. MNHN.F.50171: A, transverse section (Ts), growth limits (white arrows), diffuse parenchyma (grey arrows) and zonate parenchyma (black arrows), large black areas are cells filled with deposit material; B, Ts, growth limit with gradual transition from earlywood to latewood; C, tangential longitudinal section (Tls), 1- sometimes 2-seriate rays and parenchyma lines (arrow); D, Tls, detail of 1- sometimes 2-seriate rays; E, Tls, smooth longitudinal parenchyma walls (arrows); F, Tls, 1-2-seriate rays and tangential pits (arrows); G, radial longitudinal section (Rls), possibly cupressoid and/or podocarpoid crossfield pits (arrow); H, Rls, uniseriate radial pits; I, Rls, smooth parenchyma cell walls.Scale bars: A, C, 1 mm; B, 200 µm; E-F, H, 100 µm; G, 50 µm; I, 20 µm.